The conventional technology considered to be closest to the present invention is one disclosed in the publication of Japanese Patent No. 3128735. The principal characteristic of this technology is that one portion of a casting under a vibrating state is hit with a hammer. In this conventional technology, vibration is applied to the whole casting sand inside the casting by bringing the whole casting into a vibrating state. However, since this is not enough to separate the casting sand from the casting or to collapse the casting sand, impact is applied by a hammer to ensure satisfactory shakeout. However, the impact is applied by the hammer to only one portion of the casting, and is not applied by hitting the most effective portion. Thus, the impact applied to the casting propagates only a part of the casting, and the casting sand solidified inside the casting is only locally collapsed. Therefore, there is a problem that the casting sand over the entire portion inside the casting is not sufficiently collapsed.